Seawater carbonate chemistry and incorporation of Mg, Sr, Ba, U, and B in High-Mg Calcite Benthic Foraminifers

Measurement of elemental ratios (E/Ca) have been performed in two symbiont-bearing species of high-Mg calcite benthic foraminifers (hyaline, Baculogypsina sphaerulata and porcelaneous, Amphisorus hemprichii), cultured under five pCO2 levels, representing pre-industrial, modern and three predicted future values. E/Ca ratios were analyzed by Laser Ablation coupled with Inductively Coupled Plasma Mass Spectrometer (LA-ICP-MS). We measured several E/Ca such as Mg/Ca, Sr/Ca, Ba/Ca, U/Ca and B/Ca simultaneously. We observed that high-Mg calcite benthic foraminifers possess higher E/Ca than low-Mg calcite foraminifers, irrespective of their calcification mode (hyaline or porcelaneous). In both modes of calcification, Mg, Sr, Ba, U and B incorporation could be controlled by Rayleigh fractionation. However, more data is needed to validate and quantify the relative importance this process and closely investigate the presence/absence of other mechanism. Therefore, it highlights the need for a multi-elemental approach when looking at trace element incorporation. Finally, no significant relationship was observed between the different ratios and the pCO2 of the water, suggesting that none of the Mg/Ca, Sr/Ca, Ba/Ca, U/Ca and B/Ca is sensitive to bottom water pCO2 or pH in these species.